In order to correct maladjustments of a satellite, it is known to arrange a number of driving apparatus i.e., propulsion units on satellites. In addition to chemical driving apparatus, which eject huge masses of fuel during operation, ion engines have been employed, which must be operated over a relatively long period of time in order to obtain correction. Ion engines, as a rule, are built heavier than chemical propellants. Since ion engines eject slight amounts of noble gas, the demand of fuel to be taken along, i.e., noble gases, is smaller in terms of mass if the drive or actuator is to be capable of functioning over an extended period of time. Thus, heavier-design ion engines are opposed by the weight advantage in terms of the fuel amount to be taken along such that even heavy-design ion engines have been employed for a number of corrections in the meantime, in particular, with satellites whose operating time in space is longer than that of previous satellites.
Chemical driving apparatus of known construction, as a rule, are operated in a pulsating manner in order to correct maladjustments in that manner. What is, however, essential to the correction of maladjustments is the safe avoidance of undesired movements and, in particular, undesired rotary movements during, or on account of, the operation of the driving apparatus. The driving apparatus, therefore, must be accurately oriented, the forces of the driving apparatus having to be brought into an aligned relationship with the center of gravity of the satellite, which changes during operation. Since the position of the center of gravity itself changes, for instance, due to fuel consumption and, vice versa, also the driving apparatus are subject to changes in their axial orientation due to external influences and driving apparatus wear, the relative position of the forces acting upon operation of the driving apparatus, relative to the changing center of gravity on account of resulting movements of the satellite must be constantly detected in order to take additional corrective measures. Essential to such corrections is, however, a simple, operationally safe and lightweight-design actuation device, by means of which the desired corrections can be effected by the orientation of driving apparatus.
In addition to heavy-weight ion engines, other structural members such as, for instance, antennas or solar cells must also be oriented in case of need, wherein also a compact actuator of simple construction (and as insensitive to disturbances as possible) is required to move larger devices.
The invention aims at providing an actuation device of the initially defined kind, by which even relatively heavy satellite structural members that are to be oriented can safely be brought into the desired orientation by means of a slight number of simple and operationally safe structural members of lightweight design.
To solve this object, the configuration according to the invention essentially consists in that the actuation device comprises two independently operable linear actuators including guiding rods cardanically linked to the linear actuators and supported on, or cardanically linked to, various points of the structural member via ball-and-socket joints, as well as at least one supporting rod, wherein the supporting rod(s) are supported on, or cardanically linked to, various points both on the satellite and on the structural member to be oriented via ball-and-socket joints, and/or the structural member to be oriented is supported in, or cardanically linked to, one point directly on the satellite via a ball-and-socket joint, and that the guiding rods and the supporting rod(s) engage at points of the structural member to be oriented, that form a polygon, wherein the angular positions of the guiding rods (5, 6) relative to each other and relative to the linear drives (9, 10) are such that angular displacements of the structural member relative to the satellite are feasible about several axes. By providing two linear actuators, actuators of simple and compact design will do. By linking the guiding rods, which are connected with the linear actuators, cardanically with these actuators, even high reaction forces may be taken up without involving the risk of the actuators being destroyed. By a suitable choice of the angular positions of the guiding rods relative to the linear actuators, relatively small angular adjustments are safely feasible in several axes of space at relatively large adjusting movements of a linear actuator, the displacement path of the linear actuator naturally having to be converted into the respective correction of the angular position by calculation. The safe support of the reaction forces at a simultaneously high precision of the adjustment by small angular increments has become feasible in that the guiding rods and the supporting rod(s) engage at points of the structural member to be oriented, that form a polygon. On the whole, such an actuation device preferably is suitable for aligning ion engines to position a satellite in a largely geostationary manner out of the equator. In those cases, regular or even constant corrections are required in order to keep the satellites in the direction of the meridian, i.e., in the north-south direction, each on the northern or southern hemisphere, respectively, since the plane of the orbit passes through the plane of the equator. Ion engines bring about relatively slow corrections, the actuator, as a rule, being operated for about three hours every twelve hours. In a particularly simple manner, the linear actuators may be comprised of step motors actuating spindle drives. With spindle drives, a relatively long displacement path may, thus, be converted into relatively small angular displacements, wherein a high operating safety will be obtained in that the linear actuators are designed as spindle drives and the guiding rods are connected with the actuator so as to be pivotable about an axis intersecting with, or crossing, the spindle axis.
In a structurally particularly simple manner, the configuration may be such that the linear actuators are arranged in a common plane and, preferably, coaxial with each other, wherein the articulated connections of the guiding rods and the supporting rods with the structural member to be oriented are designed as ball-and-socket joints. In addition to the cardan joints intended for the safe absorption of the reaction forces in the region of the spindle drives, the use of ball-and-socket joints on the remaining articulation sites, thus, guarantees a high degree of precision in terms of force introduction without overstressing lightweight-design guiding or supporting rods.
According to the invention, relatively simple three-axial correction and orientation may be achieved in that a supporting rod and a further articulated supporting means of the structural member to be oriented, relative to the satellite are provided. Advantageously, each actuator cooperates with the structural member to be oriented via a four-bar arch.
In the following, the invention will be explained in more detail by way of an exemplary embodiment schematically represented in the drawings.